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Abstract:

The boundary layer transition on a 7-degree half-angle cone at zero angle of attack, with varying bluntness, is investigated experimentally in the High Density Tunnel (HDT) at the University of Oxford. The experiments are carried out in a cold Mach 6 flow, where surface heat f lux profiles are measured using infrared (IR) thermography, and the boundary and entropy layers are studied using high-speed schlieren imaging at 500 kHz. The onset of transition, XST, is identified as the location where the measured heat flux exceeds the laminar predictions based on Lees (1956). The bluntness Reynolds number, ReRN, defined using freestream conditions and the nose radius, is varied over the range 3 × 104 to 1.5 × 106. The transition Reynolds number, ReXST, increases with ReRN up to approximately 6 × 105. Beyond this value, the transition location exhibits greater scatter and a reversal trend with increasing bluntness, consistent with earlier findings by Stetson (1983) and Marineau (2014). The surface roughness profile of the nose tip is characterized, and schlieren images of the boundary and entropy layers are presented.